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United States Patent |
5,702,322
|
Sunada
,   et al.
|
December 30, 1997
|
Hydraulic pressure control system for hydraulically operated vehicle
transmission
Abstract
A system for controlling a vehicle automatic transmission, in which a gear
ratio to be shifted to is determined based on the vehicle speed and
throttle opening degree and a clutch is supplied with hydraulic pressure
such that the rotational speed of the transmission input shaft concurs
with a desired rotational speed change rate. The system includes means for
discriminating whether the engine load fluctuates and the operation is
discontinued when it is discriminated that the engine load fluctuates.
Specifically, even when the accelerator pedal is operated only somewhat
rapidly and the engine output is able to follow the change in the degree
of throttle opening, the degree of throttle opening nevertheless differs
between that at the start of gearshift and that in the course of gearshift
thereafter, causing unexpected gearshift shock to occur. The arrangement
can solve the problem.
Inventors:
|
Sunada; Satoru (Wako, JP);
Tanizawa; Shoichi (Wako, JP)
|
Assignee:
|
Honda Giken Kogyo Kabushiki Kaisha (Tokyo, JP)
|
Appl. No.:
|
610139 |
Filed:
|
February 29, 1996 |
Foreign Application Priority Data
Current U.S. Class: |
477/120; 477/154; 477/155 |
Intern'l Class: |
F16H 059/48; F16H 061/06 |
Field of Search: |
477/143,154,120,155,163,164
|
References Cited
U.S. Patent Documents
5345842 | Sep., 1994 | Kondo | 477/154.
|
5475595 | Dec., 1995 | Asahara et al. | 477/154.
|
Foreign Patent Documents |
60-231056 | Nov., 1985 | JP.
| |
2-89861 | Mar., 1990 | JP.
| |
Primary Examiner: Marmor; Charles A.
Assistant Examiner: Estremsky; Sherry Lynn
Attorney, Agent or Firm: Armstrong, Westerman, Hattori, McLeland & Naughton
Claims
What is claimed is:
1. A system for controlling hydraulic pressure of a hydraulically operated
vehicle transmission, comprising:
vehicle operating condition detecting means for detecting parameters
indicative of operating conditions of the vehicle;
gearshift command output means for determining a gear ratio to be shifted
to based on the detected parameters, to output a gearshift command;
a plurality of frictional engaging elements for selectively establishing
one gear stage in the transmission;
speed detecting means for detecting a rotational speed of at least one of a
plurality of rotational members of the transmission which changes at a
time of gearshift;
desired rotational speed change rate determining means for determining a
desired rotational speed change rate of the one rotational member based on
at least one of the detected parameters; and
hydraulic pressure control means for controlling a supply of hydraulic
pressure to at least one of the frictional engaging elements in response
to the gearshift command such that the determined gear ratio is
established to transmit engine power to a vehicle wheel, said hydraulic
pressure control means operating to control the supply of hydraulic
pressure to the frictional engaging element such that a change of the
rotational speed of the one rotational member concurs with the desired
rotational speed change rate;
wherein said hydraulic pressure control means includes:
parameter fluctuation discriminating means for discriminating whether the
at least one of the parameters fluctuates; and
said hydraulic pressure control means discontinues the operation when said
parameter fluctuation discriminating means discriminates that the
parameter fluctuates, wherein said parameter fluctuation discriminating
means discriminates fluctuation of at least one of the parameters by
calculating a difference in values of the at least one of the parameters
detected at different times.
2. A system according to claim 1, wherein the at least one of the
parameters corresponds to engine load.
3. A system according to claim 1, wherein said hydraulic pressure control
means controls the supply of hydraulic pressure to be a predetermined
value when discontinuing the operation.
4. A system according to claim 3, wherein the predetermined value is set
with respect to engine load.
5. A system according to claim 1, wherein said parameter fluctuation
discriminating means includes:
difference calculating means for calculating the difference of the at least
one of the parameters between those obtained at a different timing; and
comparing means for comparing the difference with a reference value; and
wherein said parameter fluctuation discriminating means discriminates that
the at least one of the parameters fluctuates when the difference exceeds
the reference value.
6. A system for controlling hydraulic pressure of a hydraulically operated
vehicle transmission, comprising:
vehicle operating condition detecting means for detecting parameters
indicative of operating conditions of the vehicle;
gearshift command output means for determining a gear ratio to be shifted
to based on the detected parameters, to output a gearshift command;
a plurality of frictional engaging elements for selectively establishing
one gear stage in the transmission;
speed detecting means for detecting a rotational speed of at least one of a
plurality of rotational members of the transmission which changes at a
time of gearshift;
desired rotational speed change rate determining means for determining a
desired rotational speed change rate of the one rotational member based on
at least one of the detected parameters; and
hydraulic pressure control means for controlling a supply of hydraulic
pressure to at least one of the frictional engaging elements in response
to the gearshift command such that the determined gear ratio is
established to transmit engine power to a vehicle wheel, said hydraulic
pressure control means operating to control the supply of hydraulic
pressure to the frictional engaging element such that a change of the
rotational speed of the one rotational member concurs with the desired
rotational speed change rate,
wherein said hydraulic pressure control means includes:
parameter fluctuation discriminating means for discriminating whether the
at least one of the parameters fluctuates,
wherein said hydraulic pressure control means discontinues the operation
when said parameter fluctuation discriminating means discriminates that
the parameter fluctuates,
wherein said parameter fluctuation discriminating means includes:
difference calculating means for calculating a difference of the at least
one of the parameters between those obtained at a different timing, and
comparing means for comparing the difference with a reference value, and
wherein said parameter fluctuation discriminating means discriminates that
the at least one of the parameters fluctuates when the difference exceeds
the reference value.
7. A system according to claim 6, wherein the at least one of the
parameters corresponds to engine load.
8. A system according to claim 6, wherein said hydraulic pressure control
means controls the supply of hydraulic pressure to be a predetermined
value when discontinuing the operation.
9. A system according to claim 8, wherein the predetermined value is set
with respect to engine load.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a hydraulic pressure control system for a
hydraulically operated vehicle transmission, more particularly to such a
hydraulic pressure control system which monitors the degree of throttle
opening of the vehicle engine to detect operating conditions in which the
engine output fluctuates greatly and upon detecting such a condition
suspends the clutch pressure control conducted for bringing the change in
the rotation of the transmission input shaft to the desired value.
2. Description of the Prior Art
As taught by Japanese Laid-Open Patent Application Nos. Sho 60(1985)-231056
and Hei 2(1990)-89861, it is a known practice to use a linear solenoid,
duty solenoid or the like for controlling the oil pressure of a frictional
engaging element such as a clutch or brake (referred to simply as "clutch"
hereinafter) so as to bring the change in the rotational speed of a member
whose rotation changes during gearshift, such as the change in the
rotational speed of the transmission input shaft, to a desired value.
In order to prevent gearshift shock, the clutch engaging oil pressure is
ordinarily set based on the engine output. In this prior art, the clutch
oil pressure for achieving the desired change rate or desired change is
determined based on a parameter indicative of engine load such as the
degree of throttle opening (accelerator pedal depression) so that the
determined value reflects the engine output.
This type of control involves a number of problems. For example, when the
driver stomps down on the accelerator pedal, a certain amount of time is
required for the engine output to rise to a level corresponding to the
changed degree of throttle opening. On the other hand, when the driver
very rapidly releases the accelerator pedal, the actual engine output
remains high for the degree of throttle opening owing to the continued
rotation of the engine by the inertial force up to that time.
Moreover, even when the accelerator pedal is operated only somewhat rapidly
and the engine output is able to follow the change in the degree of
throttle opening, the degree of throttle opening nevertheless differs
between that at the start of gearshift and that in the course of gearshift
thereafter. Since the desired rotational speed change or oil pressure
change is set in accordance with the degree of throttle opening in the
aforesaid clutch pressure control, unexpected gearshift shock is apt to
occur when one of the foregoing situations arises in which the engine
output does not follow the change in degree of throttle opening or the
progress of a gearshift changes in the course thereof.
SUMMARY OF THE INVENTION
An object of this invention is therefore to overcome the aforesaid problems
of the prior art by providing a hydraulic pressure control system for a
hydraulically operated vehicle transmission which determines a desired
rotational speed change constituting a desired value during gearshift,
detects change in the state of a vehicle control operation indicative of
engine load, and when the state varies, suspends clutch pressure control
for achieving the desired rotation change.
This invention achieves this object by providing a system for controlling
hydraulic pressure of a hydraulically operated vehicle transmission,
comprising vehicle operating condition detecting means for detecting
parameters indicative of operating conditions of the vehicle, gearshift
command output means for determining a gear ratio to be shifted to based
on the detected parameters, to output a gearshift command, a plurality of
frictional engaging elements for selectively establishing one gear stage
in the transmission, speed detecting means for detecting a rotational
speed of at least one of a plurality of rotational members of the
transmission which changes at a time of gearshift, desired rotational
speed change rate determining means for determining a desired rotational
speed change rate of the one rotational member based on at least one of
the detected parameters and hydraulic pressure control means for
controlling a supply of hydraulic pressure to at least one of the
frictional engaging elements in response to the gearshift command such
that the determined gear ratio is established to transmit engine power to
a vehicle wheel, said hydraulic pressure control means operating to
control the supply of hydraulic pressure to the frictional engaging
element such that a change of the rotational speed of the one rotational
member concurs with the desired rotational speed change rate. In the
system, said hydraulic pressure control means includes parameter
fluctuation discriminating means for discriminating whether the at least
one of the parameters fluctuates, and said hydraulic pressure control
means discontinues the operation when said parameter fluctuation
discriminating means discriminates that the parameter fluctuates.
BRIEF EXPLANATION OF THE DRAWINGS
The foregoing and other objects and advantages of the invention will be
more apparent from the following description and drawings, in which:
FIG. 1 is an overall view of a hydraulic pressure control system for a
hydraulically operated vehicle transmission;
FIG. 2 is an explanatory view showing a part of the hydraulic control
circuit of the system illustrated in FIG. 1;
FIG. 3 is a flowchart showing the operation of the system illustrated in
FIG. 1; and
FIG. 4 is a timing chart explaining the procedures illustrated in the
flowchart of FIG. 3.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
An embodiment of the invention will now be explained with reference to the
attached drawings.
FIG. 1 is an overall view of the hydraulic pressure control system for a
hydraulically operated vehicle transmission according to the invention.
As shown in FIG. 1, a vehicle automatic transmission T is equipped with a
main shaft MS connected with a crankshaft 1 of an internal combustion
engine E through a torque converter 2 having a lockup clutch L and with a
countershaft CS connected with the main shaft MS through multiple gear
trains.
The main shaft MS supports a main first-speed gear 3, a main second-speed
gear 4, a main third-speed gear 5, a main fourth-speed gear 6 and a main
reverse gear 7. The countershaft CS supports a counter first-speed gear 8
engaged with the main first-speed gear 3, a counter second-speed gear 9
engaged with the main second-speed gear 4, a counter third-speed gear 10
engaged with the main third-speed gear 5, a counter fourth-speed gear 11
engaged with the main fourth-speed gear 6 and a counter reverse gear 12
engaged with the main reverse gear 7 through a reverse idle gear 13.
The first gear (gear ratio or gear stage) is established when the main
first-speed gear 3 rotatably supported on the main shaft MS is connected
with the main shaft MS by a first-speed hydraulic clutch C1. Since the
first-speed hydraulic clutch C1 is also maintained in the engaged state
during establishment of the second-fourth gears, the counter first-speed
gear 8 is supported by a one-way clutch COW. The second gear is
established when the main second-speed gear 4 rotatably supported on the
main shaft MS is connected with the main shaft MS by a second-speed
hydraulic clutch C2. The third gear is established when the counter
third-speed gear 10 rotatably supported on the countershaft CS is
connected with the countershaft CS by a third-speed hydraulic clutch C3.
The fourth gear is established when the counter fourth-speed gear 11
rotatably supported on the countershaft CS is connected with the
countershaft CS by a selector gear SG and with this state maintained the
main fourth-speed gear 6 rotatably supported on the main shaft MS is
connected with the main shaft MS by a fourth-speed reverse hydraulic
clutch C4R. The reverse gear is established when the counter reverse gear
12 rotatably supported on the countershaft CS is connected with the
countershaft CS by the selector gear SG and with this state maintained the
main reverse gear 7 rotatably supported on the main shaft MS is connected
with the main shaft MS by the fourth-speed reverse hydraulic clutch C4R.
The clutches C1, C2, C3 and C4R are the aforesaid frictional engaging
elements.
The rotation of the countershaft CS is transmitted through a final drive
gear 14 and a final driven gear 15 to a differential D, from where it is
transmitted to driven wheels W, W through left and right drive shafts 16,
16.
A throttle position sensor S1 is provided in an air intake pipe (not shown)
of the engine E at a point in the vicinity of a throttle valve (not shown)
for detecting the degree of opening or position .theta.TH of the throttle
valve. A vehicle speed sensor S2 for detecting the vehicle traveling speed
V from the rotational speed of the final driven gear 15 is provided in the
vicinity of the final driven gear 15. A transmission input shaft speed
sensor S3 is provided in the vicinity of the main shaft MS for detecting
the rotational speed NM of the transmission input shaft from the rotation
of the main shaft MS, and a transmission output shaft speed sensor S4 is
provided in the vicinity of the countershaft CS for detecting the
rotational speed Nc of the transmission output shaft from the rotation of
the countershaft CS.
A shift lever position sensor S5 is provided in the vicinity of a shift
lever (not shown) installed on the vehicle floor near the driver's seat.
The shift lever position sensor S5 detects which of the seven positions P,
R, N, D4, D3, 2, and 1 has been selected by the driver. A crank angle
sensor S6 is provided in the vicinity of the crankshaft 1 of the engine E
for detecting the engine speed NE from the rotation of the crankshaft 1,
and a coolant temperature sensor S7 for detecting the engine coolant
temperature TW is provided at an appropriate location on a cylinder block
(not shown) of the engine E. Outputs of the sensors S1, etc., are sent to
an ECU (electronic control unit).
The ECU is constituted as a microcomputer comprising a CPU (central
processing unit) 17, a ROM (read-only memory) 18, a RAM (random access
memory) 19, an input circuit 20 and an output circuit 21. The outputs of
the sensors S1, etc., are input to the microcomputer through the input
circuit 20. The CPU 17 of the microcomputer determines the gear (gear
ratio) and energizes/deenergizes shift solenoids SL1, SL2 of a hydraulic
(pressure) control circuit O via the output circuit 21 so as to switch
shift valves (not shown) and thereby engage/disengage the hydraulic
clutches of prescribed gears, and controls the operation of the lockup
clutch L of the torque converter 2 via control solenoids SL3 and SL4. The
CPU 17 also controls the clutch hydraulic pressure through a linear
solenoid SL5, as will be explained later.
FIG. 2 is an explanatory view showing a part of the hydraulic (pressure)
control circuit 0 of the system of FIG. 1. Line pressure (primary
pressure) supplied from a hydraulic pressure source (not shown) is sent to
a clutch pressure control valve. The clutch pressure control valve
regulates, with the aid of aforesaid linear solenoid SL5, the line
pressure within a prescribed throttle pressure range and supplies it to
the clutches C1, C2, C3 and C4R. An accumulator is provided in the path to
absorb surge pressure.
Thus, in this embodiment, the CPU 17 regulates the line pressure by using
the linear solenoid SL5 to control the clutch pressure control valve so
that, as explained later, the pressures supplied to the clutches are
controlled to the desired value. As shown in FIG. 2, each of the clutches
C1, C2, C3 and C4R is provided with a hole 100 for discharge of
centrifugal hydraulic pressure. Centrifugal pressure is discharged at the
time of clutch release, through a check valve (not shown).
FIG. 3 is a main routine flowchart showing the operation of the hydraulic
pressure control system according to the invention. The explanation of
this figure will, however, be preceded by an explanation with reference to
FIG. 4.
FIG. 4 is a timing chart of the clutch pressure control in the system. As
shown in this figure, when gearshift is not in progress the desired clutch
pressure is controlled in open-loop manner to a value determined in
advance for the gear (gear ratio) concerned and the degree of throttle
opening (degree) .theta.TH.
At the start of a gearshift, (operating) oil is supplied up to time T0 for
taking up clutch play, and after the play has been taken up, control for
maintaining the oil at low pressure and control in the torque phase are
conducted. This is indicated as "Response pressure (preparation for low
pressure)" in the figure.
The period from time T0 to time T1 corresponds to the inertial phase. As
explained earlier, in this phase the clutch pressure is controlled in a
closed-loop manner so as to bring the change in the rotational speed of a
member whose rotation changes during gearshift, such as the change in the
rotational speed of the transmission input shaft (main shaft rotational
speed NM), to a desired value.
At the end of the inertia phase, between times T1 and T2, (indicated in the
figure as the "End-period mode"), the clutch pressure is feedback
controlled for maintaining the clutch pressure especially just before the
completion of the gearshift so as to terminate the gearshift smoothly. In
the period between times T2 and T3 shown as the "Termination mode" in the
figure, the clutch pressure is controlled in open-loop fashion so as to
gradually increase the oil pressure toward a value determined in advance
for the gear ratio after gearshift and the degree of throttle opening
.theta.TH.
The characteristic feature of this system is not directed to the control
described in the foregoing, however, but to a system which detects change
in the state of a vehicle control operation indicative of engine load,
specifically operation (manipulation) of the accelerator pedal, and when
the state varies greatly between the start of the response pressure
(preparation for low pressure) mode and the end of the termination mode,
suspends the control shown in the figure and conducts control in open-loop
manner for bringing the oil pressure to a value determined in advance for
the gear ratio and the degree of throttle opening .theta.TH.
The operation of the control system will now be explained with reference to
the flowchart of FIG. 3. This routine is activated at a timing of once
every 20 ms, for example.
First, in S10, it is checked whether gearshift is in progress, i.e.,
whether the gearshift command shown in FIG. 4 has been issued or output.
FIG. 4 shows an example of issuance of a shift signal for an upward shift
from second to third gear.
When the result in S10 is NO, the program goes to S12, in which, as
described in the foregoing, the clutch pressure is controlled in open-loop
fashion to bring it to a value determined for the detected degree of
throttle opening .theta.TH in accordance with the predetermined
characteristics for the gear (second gear in this example), and the
routine is once terminated.
If, when the routine of FIG. 3 is reactivated 20 ms later, the state is one
at or after the time point indicated as "Gear-shift" in the timing chart
of FIG. 4, the result in S10 becomes YES, and the program goes to S14, in
which it is checked whether a change has occurred in the gear ratio Gr.
The gear ratio Gr is calculated as:
Gr=Transmission output rotational speed NC1/Transmission input rotational
speed NM.
S14 checks whether a change has occurred in the gear ratio Gr calculated
according to this equation, and when the result is NO, the program goes to
S16, in which it is checked whether the time T0 has passed. When S16 finds
that the time T0 has not passed, the program goes to S18, in which it is
checked whether the change in the degree of throttle opening .theta.TH is
large (or fluctuating greatly).
This check is made by calculating the first-order difference between the
detected values of the degree of throttle opening .theta.TH in the current
and preceding cycles and comparing the result with an appropriately set
reference value. When it is found that the difference exceeds the
reference value, it is discriminated that the change in the degree of
throttle opening .theta.TH is large (in other words the throttle opening
.theta.TH is fluctuating).
As explained earlier, the purpose of the control according to this
embodiment is to eliminate the problems arising when, for example, the
engine output cannot keep up with changes in the degree of throttle
opening. The reference value is therefore appropriately selected to be of
sufficient magnitude for detecting changes in the degree of throttle
opening large enough to cause such problems.
When S18 finds the change in the degree of throttle opening .theta.TH to be
large, the program goes to S12, in which, for the reason just explained,
the same control as when gearshift is not in progress is conducted,
namely, the clutch pressure is controlled in open-loop fashion to bring it
to the value determined for the detected degree of throttle opening
.theta.TH in accordance with the predetermined characteristics for the
gear (gear ratio), and the routine is once terminated.
The reason for this is that in a control system which, as explained in the
foregoing, controls the clutch pressure during gearshift in accordance
with a parameter such as the degree of throttle opening or other indicator
set based on engine load so as to reflect the engine output, use of a
degree of throttle opening that does not accurately indicate the engine
load is liable to degrade rather than improve the control performance and
lead to the occurrence of gearshift shock. In this embodiment, therefore,
this problem is overcome by conducting the same clutch pressure control as
when no gearshift is in progress when the change in the degree of throttle
opening is great.
On the other hand, when S18 does not find that the change in the degree of
throttle opening is large, the program goes to S20, in which the clutch
pressure is open-loop controlled in accordance with the response pressure
mode. More specifically, the processing indicated as "Response pressure
(preparation for low pressure)" shown in the timing chart of FIG. 4 is
conducted from the start of gearshift to time T0.
In the next and following routine cycles, when S16 finds that the time T0
has passed, the program goes to S22, in which it is checked whether the
gear ratio Gr is equal to or greater than a prescribed value Ga (shown in
FIG. 4). When the result in S22 is NO, the program goes to S24, in which
it is checked whether the time T1 has passed. When the result in S24 is
NO, the program goes to S26, in which the aforesaid decision is again used
to check whether the change in the degree of throttle opening .theta.TH
detected at that time is large. When the result is YES, the program goes
to S12, in which, for the reason explained earlier, the same control as
when gearshift is not in progress is conducted, and the routine is once
terminated.
On the other hand, when S26 finds that the change in the degree of throttle
opening .theta.TH detected at that time is not large, the program goes to
S28, in which feedback control is conducted. In other words, as shown by
the inertia mode in the timing chart of FIG. 4, the clutch pressure
(specifically, the oil pressure of the clutch C3 on the engagement side in
the example) is feedback controlled to bring the change rate of the
transmission input rotational speed NM to the desired value, e.g. a
constant value.
The relationship between the gear ratio and time is shown in FIG. 4.
Specifically, at the start of the gearshift, the gear ratio Gr remains at
a value corresponding to second gear for a short time. Then when the
supply of oil to the second-speed clutch C2 is stopped in response to the
gearshift command, the second-speed clutch begins to slip and the gear
ratio gradually changes from that corresponding to second gear. The time
point at which this changes starts is detected from the gear ratio Gr.
Since the system according to the invention is equipped with a timer
(designated in the figure as "System timer"), it is also possible to
detect this time point by clocking the passage of time T0 from the start
of gearshift. In the flowchart of FIG. 3, it is detected from both the
gear ratio and time passage. The step of confirming time passage in S16 is
therefore skipped when S14 finds that a change has occurred in the gear
ratio Gr.
In the next and following routine cycles (program loop), when S22 finds
that the gear ratio Gr has exceeded the prescribed value Ga, the program
goes to S30, in which it is checked whether the gear ratio has reached the
gearshift ending gear ratio Gr. As shown in FIG. 4, the gearshift ending
gear ratio Gr is a value corresponding to the gear ratio in the
destination gear (third gear in this example). The check in S30 therefore
amounts to checking whether the third-speed clutch C3 has reached the
engagement time point (shown as T2 in FIG. 4).
When S30 finds that the gear ratio has not reached the gearshift ending
gear ratio GR, the program goes to S32, in which, by way of confirmation,
it is checked from the value of the system timer whether the time T2 for
reaching the gearshift ending gear ratio has been reached. When the result
is NO, the program goes to S34, in which it is checked in the same manner
as that described earlier whether the change in the degree of throttle
opening .theta.TH detected at that time is large. When the result is YES,
the program goes to S12, in which, for the reason explained earlier, the
same control as when gearshift is not in progress is conducted, and the
routine is once terminated.
On the other hand, when S34 finds that the change in the degree of throttle
opening .theta.TH is not large, the program goes to S36, in which the
control according to the end-period mode discussed earlier with reference
to FIG. 4 is conducted and the routine is once terminated.
In the next and following routine cycles, when S30 finds that the gearshift
ending gear ratio has been reached or S32 finds that the time T2 has
passed, the program goes to S38, in which it is checked whether the time
T3 has passed. When the result is NO, the program goes to S40, in which it
is again checked whether the change in the degree of throttle opening
.theta.TH detected at that time is large. When the result is YES, the
program goes to S12, in which, for the reason explained earlier, the same
control as when gearshift is not in progress is conducted, and the routine
is once terminated. When the result is NO, the program goes to S42, in
which the clutch pressure control according to the termination mode
discussed earlier with reference to FIG. 4 is conducted.
When S38 finds that the time T3 has passed, since this means that the
gearshift is finished, the program goes to S12, in which the control for
when gearshift is not in progress is resumed.
As clearly shown in FIG. 3, in S24 and S32, when it is found that time T1
and T2 have passed, respectively, the program goes to S32 and S38,
respectively.
As explained in the foregoing, this embodiment detects whether the change
in the degree of throttle opening .theta.TH is large, and when the result
is affirmative, conducts the control for when gearshift is not in
progress, namely, controls the clutch pressure in open-loop fashion to
bring it to the value determined for the detected degree of throttle
opening .theta.TH in accordance with the predetermined characteristics for
the gear ratio. As a result, occurrence of gearshift shock is avoided even
when the degree of throttle opening does not accurately indicate the
actual engine load.
While the embodiment uses the degree of throttle opening as a parameter
indicating the engine load, the engine load can instead be detected from
the amount of accelerator pedal manipulation, the intake air pressure, the
intake air mass or the like.
While the foregoing description is made taking a hydraulically operated
transmission as an example, the invention can also be applied to other
types of vehicle transmissions.
While the invention was described with respect to a hydraulically operated
transmission, it can also be applied to other types of vehicle
transmissions.
Although the invention has thus been shown and described with reference to
specific embodiments, it should be noted that the invention is in no way
limited to the details of the described arrangements, changes and
modifications may be made without departing from the scope of the
invention, which is defined by the appended claims.
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